Printed circuit boards (PCBs) are typically made of multiple layers of insulated and conductive materials. Electronic components are mounted to the PCB to form a printed circuit board assembly (PCBA). To mount an electronic component to the PCB, an electronic component includes components leads, or pins, which are inserted into plated through-holes (PTH) in the PCB. The leads are then mechanically and electrically connected to the PCB, such as by a filling the plated through holes with solder. Most PTH component leads are required to a specific lead length protruding from the back of the PCB per the industrial standard or customer specification. Even though most of the lead can be pre-trimmed at a preforming stage, it is usually necessary to trim the lead length to the required specification after mounting and soldering to the PCB to avoid solder short to the further assembly, for example a metal casing.
In the case of a single-sided PCB, components are mounted only on the top surface and a lead trimming machine is used to trim all the leads protruding from the back surface of the PCB in one single pass, as there are no components mounted on the back surface to interfere with this single pass process.
Surface mount technology (SMT) is an alternative mounting process where components are mounted or placed directly onto the surface of printed circuit boards (PCBs). Contacts on the component are mounted to corresponding contact pads on the surface of the PCB. A component may include short pins or leads of various styles, flat contacts, a matrix of solder balls (BGAs), or terminations on the body of the component for interconnecting with the corresponding contact pads on the PCB. Although SMT has largely replaced PTH technology for mounting components to a PCB, mixed technology applications are common where components are mounted to a common PCB using both SMT and PTH technology.
In many mixed technology applications, components are mounted on both surfaces of the PCB. Components mounted using PTH technology still require lead trimming. However, other components mounted onto the same surface of the protruding leads to be trimmed prohibit the use of the single pass process. Instead, a manual process is performed where a person using a lead trimming cutter manually cuts the protruding leads interspersed amongst the SMT components.